Olefinic hydrocarbons such as, for example, propylene and butylene, are one of the major building blocks of a large number of petrochemical products. Such olefinic hydrocarbons are also useful in petroleum refineries for the production of motor fuel blending components. In view of the commercial desirability of such olefinic hydrocarbons, there is a continuing search for techniques to lower the cost of production and increase the relative yield of such olefins.
One process for producing olefins such as, for example, propylene, involves the catalytic dehydrogenation of a dehydrogenatable hydrocarbon-containing feedstock such as, for example, a propane-containing feedstock. Such catalytic dehydrogenation processes generally involve mixing the dehydrogenatable hydrocarbon-containing feedstock with a hydrogen-rich gas stream and introducing the combined feedstock into a reactor section, typically including several reactor units connected in series, wherein at least a portion of the dehydrogenatable hydrocarbons in the combined feedstock are catalytically converted to produce a reactor effluent stream containing at least a corresponding olefin product. Generally, such dehydrogenation reactor effluent streams have a temperature in excess of about 150° C. (about 300° F.).
Such dehydrogenation reactor effluent streams are subsequently cooled and compressed to facilitate separation into individual product streams. Dehydrogenation reactor effluent streams can be cooled using various heat exchange methods such as, for example, indirect heat exchange with a cooling medium such as, for example, cooling water. One such indirect heat exchange method generally involves passing the hot dehydrogenation reactor effluent stream through a heat exchange unit such as, for example, a tube and sheet heat exchanger, to produce a cooled effluent stream having a temperature profile that is suitable for efficient compression.
However, such indirect heat exchange units can be susceptible to fouling by constituents of the dehydrogenation reactor effluent stream. For example, heavy hydrocarbon compounds (i.e., C7+ hydrocarbons) contained in the dehydrogenation reactor effluent stream can condense on surfaces of the heat exchange unit which can result in a reduction of the cooling capacity of the heat exchange unit. Generally, the temperature of a gas to be compressed determines, at least in part, the capacity of an associated compressor, i.e., the higher the temperature of the gas the less it can be compressed. Thus, reducing the cooling capacity of the heat exchange unit results in a reduced compression capacity in an associated compressor which can, in turn, result in increased down time for cleaning of the heat exchange units and decreased product output.
In view of the above, there is a need and a demand for processing schemes and/or arrangements effective to reduce fouling of heat exchange units used to cool dehydrogenation reactor effluent streams.
Additionally, gaseous materials which pass through such indirect heat exchange units can also experience a significant pressure drop from inlet to outlet resulting in a cooled product stream being at a pressure which is lower than may be desired and can require additional energy expenditures to compress the cooled product stream to a pressure suitable for further processing in subsequent separation units. Thus, there is a further need and a demand for processing schemes and/or arrangements that result in reduced pressure drop across the heat exchange unit.
Further, a pressure drop across the heat exchange unit can result in an increased pressure at an associated dehydrogenation section outlet which can cause reductions in the yield of olefins, such as propylene, produced by the dehydrogenation process. Accordingly, there is a still further need and a demand for processing schemes and/or arrangements effective to result in an increased relative yield of olefins, particularly, propylene.